Anyone know offhand what size filler block I need for the rear sight dovetail on a 1956 99F, 7825XX S/N range? Maybe its called a slot blank? is there a standard size?

I'm putting a Williams Foolproof tang mount sight on, and it looks like I need to remove the original barrel mounted rear sight to get a decent view.
BTW, tried mounting a Redfield 70L first, but it didn't clear the stock, and I don't want to notch the stock for it to fit.

Thanks

Last edited by MikeL2; 10/06/22.